Methods and systems for measuring brain activity

ABSTRACT

The invention encompasses systems and methods allowing for minimally invasive insertion and functional optimization of implantable electrode arrays designed for placement within the subgaleal space to record brain electrical activity. The implantable arrays comprise a support structure capable of being implanted in the subgaleal space and comprising at least one reference element; at least one ground element; and one or more recording elements; and wherein said array is capable of detecting and/or transmitting a subgaleal electrical signal.

FIELD OF THE INVENTION

The invention encompasses systems and methods allowing for minimallyinvasive insertion and functional optimization of electrode arraysdesigned for temporary placement within the subgaleal space to recordbrain electrical activity. The described systems and methods allow ahealth care provider, even without specialized EEG or surgical training,to record and compare clinically relevant bihemispheric high-fidelityEEG signals in the acute setting without the need for application ofscalp electrodes or implantation of recording electrodes in a formalsurgical setting.

DISCUSSION OF THE RELATED ART

In the following discussion, certain articles and methods will bedescribed for background and introductory purposes. Nothing containedherein is to be construed as an “admission” of prior art. Applicantexpressly reserves the right to demonstrate, where appropriate, that thearticles and methods referenced herein do not constitute prior art underthe applicable statutory provisions.

In many cases of brain injury, timely detection of deleterious changesin brain health can be critical for effectively treating a primaryinjury or preventing a secondary injury. Although a range ofneuromonitoring devices have been developed for these purposes, the mosteffective means of quickly and directly evaluating neuronal health iselectroencephalography (EEG).

Traditional EEG utilizes a series of metallic electrodes that areaffixed to a patient’s scalp to record oscillatory electrical potentialsnaturally generated by specific cells within the brain. Although EEG haslargely been used in the past for the purposes of detecting abnormalfiring of neurons resulting in seizures, data has also supported the useof EEG for real-time monitoring of brain health in normal andpathological states.

For example, EEG changes are rapidly observed when cerebral blood flowdrops below a critical level (cerebral ischemia). In many cases thesechanges can be seen prior to the development of irreversible braindamage (cerebral infarction), which allows a health care provider toperform a clinical intervention to improve brain blood flow and preventpermanent damage. Along these lines, EEG could be extremely beneficialfor patients suffering from traumatic brain injury, cardiac arrest,stroke, and other acute neurological disorders in which delayed,reversible changes in brain health can occur and effective real-timemonitoring of brain health would provide the opportunity for moreeffective and appropriate clinical intervention.

Despite major benefits that could be attributed to the use of EEG inpatients with acute brain injury, practical factors have significantlylimited the widespread adoption and utility of this technique for acutebrain injury in the clinical setting. Such factors have concurrentlylimited development of approaches for automated EEG data analysis, whichin the modern era is essential for continuous clinical use.

Traditional EEG is extremely technically cumbersome. To initiaterecording of EEG data, a first step requires application of metal-basedelectrodes to the patient’s scalp by a trained technician. This processis time consuming, tedious, and often needs to be repeated for patientsthat require prolonged monitoring and undergo various clinicalinterventions (as the electrodes tend to be easily dislodged due to thelack of a permanent fixative agent between electrode and skin).Effectively attaching the electrodes to the recording hardware requiresnumerous individual wires that are plugged into specific points on thesignal amplifier (requiring specialized knowledge and experience). Thisrequirement for a large number of individually attached wires results inchallenges for streamlined care and leads to frequent disconnections andfrustrations for caregivers.

An additional technical requirement for standard scalp electrode-basedEEG is that a discrete “reference” electrode be used to record abaseline electrical signal against which all other recording channelsare measured. This reference electrode is accompanied by a necessarysecond “ground” electrode which serves to provide common-mode rejectionof electrical artifact generated by the hardware or electrical equipmentin the local environment. Should the reference electrode, groundelectrode, or both be poorly positioned or become disconnected in somefashion, the entirety of the EEG recording becomes corrupted andunusable. Thus, a trained technician must be available to constantlymonitor the fidelity of an EEG recording and provide “troubleshooting”support should there be technical issues with the common reference orground electrodes.

For these reasons, 24-hour availability of highly-trained technicians isrequired to effectively utilize scalp-based continuous EEG recording forbrain injured patients. Unfortunately, the significant majority ofclinical centers do not have the financial resources or access totrained personnel to support this process and are therefore unable toeffectively offer continuous 24-hour EEG recording for brain injuredpatients.

Beyond the complicated technical requirements associated with long-termscalp electrode-based recording, current clinical use of EEG is largelydependent on raw electrical waveform analysis. This process requires theavailability of an expert trained in the art of EEG interpretation.There are several major limitations associated with the need for such atrained expert. First, these individuals generally do not review the EEGon a continuous basis; rather, recordings are reviewed on an episodicbasis which may be as infrequent as once every 24 hours. Such infrequentEEG review provides little utility for monitoring brain health inpatients with neurological injuries, as relevant physiological changesare generally continuous rather than episodic. Second, concerning EEGchanges that are identified in delayed fashion are often noted wellafter a potentially reversible secondary brain injury has becomeirreversible, therefore rendering delayed identification of the EEGabnormality clinically meaningless. Third, experts trained in the art ofEEG interpretation are relatively rare in number and are unavailable inmany settings where EEG monitoring for brain injured patients iscritically important. Finally, a great deal of information that is ofgreatest utility for monitoring patients with brain injury cannot be seein the raw waveform data and requires quantitative analysis of EEG“power” in specific frequency bands to effectively identify changes ofconcern.

To this end, it is possible that physiologically useful information canreadily be gained through use of mathematical processing of raw EEGsignals into easily interpreted visual color displays (“CompressedSpectral Arrays” displaying EEG power in discrete frequency bands).However, requirements for a “clean” EEG signal (that which benefits froma high signal-to-noise ratio) in such analysis has terminally mitigatedthe clinical adoption of quantitative EEG methods using scalp-basedelectrodes. Current methods require human oversight to confirm thevalidity of processed signals and ensure that periods of contaminationfrom artifact, noise or loss of electrode contact are not interpreted asvalid EEG (which as previously noted is common with scalp EEG).

Moreover, contaminated EEG recordings can emerge from severalindependent sources. On the “signal” side of the equation, distance fromthe “generators” of the EEG signal (i.e. the neurons) and the presenceof intervening tissue that dampens the signal (e.g. tissues of thescalp) serve to decrease electrical signal amplitude and increase“averaging” effects that tend to minimize overall amplitude of the EEGwaveform. On the “noise” side of the equation, electromechanical factorsinherent to recording with scalp electrodes are significant sources ofEEG artifact. As mentioned previously, the tenuous connection betweenmetal and skin results in the introduction of significant electricalnoise and inconsistency of signal. Sources of external electrical noiseare widely distributed in clinical settings in which care ofbrain-injured patients typically occurs (e.g. the intensive care unit)and can include a diverse array of environment-based electricalartifacts (contaminating electrical signals from other equipment,movement of the electrodes or connecting wires during clinical careactivities, etc) and patient-based artifacts (electrical signalsgenerated by muscle activity associated with shivering, abnormalities ofthe skin, etc). Critically, excessive noise, failure or loss of thecommon reference electrode will prohibit any useful recording from anyadditional electrodes spread over the cranium.

Taken together, poor signal-to-noise ratio and poor long-term fidelityof scalp-based EEG systems has precluded the development of effectiveautomated, continuous, reliable quantitative analysis which is essentialfor an EEG-based neuromonitoring tool in brain injured patients.Therefore, a system is needed that allows non-expert clinical personnelto deploy electrode arrays that provide continuous high-fidelity EEGrecording.

BRIEF DESCRIPTION OF THE INVENTION

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key or essentialfeatures of the claimed subject matter, nor is it intended to be used tolimit the scope of the claimed subject matter. Other features, details,utilities, and advantages of the claimed subject matter will be apparentfrom the following written Detailed Description including those aspectsillustrated in the accompanying drawings and defined in the appendedclaims.

As described herein, one aspect of the invention is an implantablesubgaleal electrode array comprising a support structure capable ofbeing passed through the skin and implanted in the subgaleal space. Thesupport structure of the implantable device comprises at least onereference element; at least one ground element; and one or morerecording elements. This array is capable of detecting and/ortransmitting a subgaleal electrical signal.

In preferred embodiments, multiple recording elements are included inthe array. These multiple recording elements can be used as “back-ups”in the event that one of the recording elements becomes inactive and/orare unable to transmit accurate EEG signals. Moreover, the position ofthe recording elements along the support structure can vary. Forexample, the recording elements can be arranged linearly and/orcircumferentially along the support structure. In other preferredembodiments, the reference and the ground elements can be located at themost distal contact from the array exit point.

In further preferred embodiments, the reference and/or the groundelement is located just proximal to an array exit point (e.g. just belowthe skin). In further preferred embodiments the reference and groundelements are distributed along the array at some distance from an entryor exit point of the array. In addition, the reference and/or the groundelements can be located on contralateral arrays or collocated on thesame array. In further preferred embodiments, the reference and groundelements may be present in other configurations that are distinct fromthe array encompassing the recording elements; for example, thereference element, ground element or both may be located upon anotherdevice designed for implantation into or on the patient. The recordingelements can be distributed along the array and may be positionedproximal to, distal to, or intermingled with the reference elements,ground element, or both. In further preferred embodiments, parallelreference and ground electrodes are electrically tied together from eachside at the level of the external hardware, resulting in “average”ground signal and reference signal for subsequent analysis of symmetry.Any of the above combinations are also envisioned.

The support structure of the implantable array must be made of amaterial capable of housing the reference, ground and recordingelements. More importantly, the support structure must be capable ofinsertion into the subgaleal space and maintained for an extended periodof time (ranging from several minutes up to several weeks). Example ofpreferred support structures, include but are not limited to beingcylindrical in shape, made of flexible biocompatible material (such as,for example silastic or polyurethane); and/or curved in shape with apointed tip. The diameter of the array may be as small as 0.5 mm, 0.6mm, 0.7 mm, 0.8 mm, 0.9 mm, or 1.0 mm and as large as 1 cm, 2 cm, or 3cm, although smaller or larger arrays are also possible. In cases wherethe array may be curved it would be generally intended to follow thenatural curvature of the human skull and therefore would be flexible incertain cases. These structural characteristics of the support structurefacilitate atraumatic passage of the array through the skin and into thesubgaleal space.

As described herein, the implantable electrode array can comprisefurther elements to aid in the insertion, positioning and/or maintenanceof the array in the subgaleal space. For example, equipment associatedwith the implantable electrode array may further comprise a sheath, aneedle and a passage assistant attachment wherein said attachment meansis capable of pushing and/or pulling the needle through the subgalealspace; an insertion guide for identifying the anatomically appropriatearea for electrode entry; a retention means of the electrode at the skinentry site; a retention means of the electrode at the skin exit site; anexit guide to facilitate passage of a needle through the skin at theexit point; a needle physically associated with, connected to orotherwise part of the electrode array; and/or any combination of above.

In preferred embodiments, the electrode array is capable of beingdirectionally tunneled in the subgaleal space in the parasagittalanterior-posterior line overlying one or both hemispheres of the brain.

In other embodiments, the implantable array is part of a system used tomeasure subgaleal activity. For example, the system for measuringsubgaleal activity can comprise both the implantable subgaleal electrodearray as described herein along with an interface connecting saidimplantable subgaleal electrode array to a processor. The processor canbe configured to perform a number of tasks and calculations, includingbut not limited to:

-   a) detecting, filtering, processing, displaying, storing and/or    transmitting brain-derived electrical signal in real time;-   b) automating the selection of the reference element and/or the    ground element;-   c) interrogating the recording function of the reference element,    the ground element and the recording element;-   d) filtering and/or processing the detected electrical signals to    generate uni- or multichannel electroencephalographic (EEG) data,    preferentially including:    -   (i) raw EEG data; or    -   (ii) quantitative EEG data;-   e) utilizing a range of display and recording montages including    referential montages and montages derived from pairs of electrodes;-   f) preassigning a recording montage to one or more recording    elements;-   g) continuously monitoring, identifying and excluding a reference    element, ground element and/or recording element demonstrating poor    signal quality, preferentially using techniques such as;    -   (i) evaluation of absolute voltage;    -   (ii) evaluation of voltage relative to other individual or        aggregated recording elements;    -   (iii) evaluation of absolute EEG power;    -   (iv)evaluation of EEG power relative to other individual or        aggregated recording elements;    -   (v) impedance measurement of recording elements;-   h) analyzing and interpreting signals between multiply implanted    electrode arrays;-   i) balancing montages, preferentially through selection of data from    specific recording elements to provide symmetry between arrays;-   j) allowing for variable or dynamic selection of specific    combinations of recording elements on multiple arrays to make a up a    recording or display montage;-   k) performing bipolar mathematical referencing between the recording    elements on an array;-   l) measuring, analyzing and reporting symmetry, asymmetry or    difference analysis between the two hemispheres of the brain;-   m) any combination of (a)-(l).

Preassigning a recording montage to one or more recording elements canoccur either by user selected combination of implanted arrays or bydirect interrogation of the electrical signals/data received. Moreover,by continuously monitoring, identifying and excluding non-functionalreference, ground and/or recording elements allows one to evaluatesignal characteristic for each individual recording element and discarddata from a specific recording element should it be deemed to benonfunctional or artifactual.

Similarly, by using multiple implanted electrode arrays positionedbilaterally (for example), one can receive symmetrical analysis ofhemispheric recordings, such that symmetry or difference analysisbetween the two hemispheres of the brain can be generated and evaluated.Moreover, by allowing for variable or dynamic selection of specificcombinations of recording elements on multiple arrays to make a up arecording or display montage provides greater diversity of recordedintercontact electrical signal.

In preferred embodiments, the electrode array is capable of beingdirectionally tunneled in the subgaleal space in the parasagittalanterior-posterior line overlying one or both hemispheres of the brain.

In other embodiments, the interface and the processor are integratedinto each other or the array, and/or portable. Additionally, theretention element and/or the stopper are integrated with the interfaceand/or processor,

In further preferred embodiments, the implantable electrode array and/orthe system as described herein is used to measure brain activity. Brainactivity can be measured in a number of in conditions, including, butnot limited to brain injury, stroke, cerebral hemorrhage, intracranialhemorrhage, hypoxic/anoxic brain injury, such as, for example, as may beseen with cardiac arrest, seizure, a critical neurological injury,and/or any medical condition requiring brain monitoring.

In further preferred embodiments the system described herein can be usedto detect spreading depression of the cerebral cortex.

Moreover, in further preferred embodiments, the implantable electrodearray and/or the system as described herein can be used to:

-   a. measure brain activity during an endovascular procedure;-   b. measure brain activity during a neurosurgical or vascular    surgical procedure;-   c. measure brain activity during a cardiac or other surgical    procedure;-   d. assess brain injury in an acute setting, such as, for example, in    an ambulance or battlefield;-   e. identify laterality of brain injury or abnormality;-   f. provide diagnostic information about brain health; or-   g. any combination of (a)-(f).

DESCRIPTION OF THE DRAWINGS

The objects and features of the invention can be better understood withreference to the following detailed description and accompanyingdrawings.

FIGS. 1A and 1B depict the anatomic position of a subgaleal electrodearray placed in the parasagittal plane in the midpupillary line on theright side (100), extending from the posterior/parietal insertion point(110) to the anterior/frontal exit point (120), with an extracranialextension designed for unitized insertion into a connection cable thatconnects to the interface/processor (130). The gray portion of the arrayis that which is located within the subgaleal space.

FIG. 2 is a graphical “cutaway” representation of the layers of thescalp, including epidermis (200), subcutaneous tissue (210), galea(220), subgaleal space (230), and skull (240), demonstrating anelectrode array (250) within the subgaleal space between the galea andthe skull after having been placed through the skin and subcutaneoustissues (200, 210, 220).

FIGS. 3A, 3B and 3C depict needle devices, each with attached sheath(310), designed for atraumatic passage of an electrode array into thesubgaleal space. Three different needle examples are shown in FIGS. 3A,3B and 3C, 300, 320 and 330 respectively. The needle tip may be straight(320) or angled (330) to facilitate passage through the subgaleal spaceas is illustrated in FIGS. 3B and 3C. The needle itself may be curved toconform to the natural curvature of the skull as is indicated by needleportion (340) shown in FIG. 3C.

FIGS. 4A, 4B and 4C illustrate the points of attachment and means of usefor the needle passage assistant in relation to the needle and sheathapparatus for subgaleal array positioning; holes are present at thefront (400) and back (410) of the needle through which the passageassistant can be placed for “push” (420) and “pull” (430) assistance.

FIG. 5 provides a top-down view of a head with symmetric bilateralelectrode arrays placed in the subgaleal space in the parasagittalmidpupillary line (500) overlying the parietal (510) and frontal (520)regions.

FIGS. 6A, 6B and 6C demonstrate characteristics and means of use for aneedle exit guide (600) designed to assist with needle passage through aproposed point of egress from the subgaleal space.

FIG. 6A is a face-on view of the exit guide (600) having a solid ringwith a central opening (610) for passage of the needle.

FIG. 6B is a side cutaway view of the exit guide (600) having a taper inthickness from the outer edge (630) to the rim of the central hole(640).

FIG. 6C is a top down view of the head (650) and demonstrates aneedle/sheath apparatus being placed through the subgaleal space withthe exit guide (600) positioned at the proposed exit point to direct andassist exit of the needle from the subgaleal space.

FIGS. 7A and 7B provide lateral and top-down views respectively of aneedle insertion guide (700), designed to identify the appropriatetrajectory in the midpupillary line (710) and an entry point at theparietal curvature of the skull (720).

FIGS. 8A to 8G depict array retention devices to assist with securing anarray that has been placed into the subgaleal space.

FIGS. 8A and 8B are face-on and side views respectively of an exemplaryposterior “stopper,” 805 consisting of a small hollow cylindricalcentral element attached to a larger disc that will attach to the end ofthe array and designed to prevent pull-out of the array from theanterior exit point, which can be placed on the posterior end of thearray prior to insertion (820) and secured to the skin after the finalrecording element on the array has passed into the subgaleal space(830).

FIGS. 8C and 8D are, face-on (840) and side (850) views respectively ofan exemplary anterior “stopper,” consisting of a disc with a centralhole just large enough to accommodate passage of the array through thehole and designed to prevent posterior movement of an implanted arrayback into the subgaleal space, which can be placed over the anterioraspect of the array (860) following passage of the array through theanterior exit point (870). The retention devices can be secured usingstaples, sutures or alternate medically appropriate means to secure themto the skin, and once secured in place the retention devices will serveto stabilize the array within the subgaleal space as well as maintainsterility be providing coverage for the entry and exit points into theskin.

FIGS. 8F and 8G are sequential top-down views of a head with anelectrode array placed in the subgaleal space and shows positioning ofposterior stopper (830) and subsequently anterior stopper (870) afterarray insertion.

FIG. 9 depicts a unitized assembly by which the insertion needle is apart of the electrode array (900) and includes a retention elementdistal to the last recording element designed to secure the array at thepoint of entry into the scalp (910).

FIGS. 10A and 10B provide a representative example of numerical channelassignments for bilateral subgaleal electrode arrays including ground(numbers 10 and 20), reference (numbers 9 and 19), and individualrecording elements (remaining contacts).

FIGS. 11A and 11B provide a representative example of channelassignments for a unilateral subgaleal electrode array including ground,reference and individual recording elements, in this case using analternate arrangement of reference (number 5) and ground (number 10)positioning in relationship to the remainder of recording elements onthe array.

FIGS. 12A, 12B and 12C depict strategies for selecting recording channelpairs to generate synthetic channels in a bipolar recording montage. InFIG. 12A, synthetic channels are generated from bipolar comparisons ofrecording from adjacent channels, resulting in a total of 7 totalsynthetic channels. FIG. 12B represents a “skip one” approach wherebysynthetic channels are generated from bipolar comparisons of every otherrecording element along the array. Similarly, FIG. 12C exhibits a “skiptwo” approach whereby synthetic channels are generated from bipolarcomparisons of every third recording element along the array. The “skip”synthetic channels can thus be used to provide electrographic samplingof larger recording fields.

FIG. 13 provides a lateral view of a subgaleal array with integratedneedle and stopper device (1300) which is inserted and secured at asingle entry point (1310) in the frontal region without need for asecondary exit point. The gray portion of the array indicates that whichis located within the subgaleal space.

FIG. 14 depicts examples of the balancing function of the processor,which allows for maintenance of data symmetry between the two cerebralhemispheres in cases where an individual recording element at a specificpoint along a single array are identified as “bad. In thisrepresentative example, data from bilateral arrays including fourrecording elements each are utilized. When a particular data channel isidentified as “bad” on one array (in this case, a series of “bad”channels on the right side), the processor provides concurrent exclusionof 1) the derived synthetic bipolar recording channels containing the“bad” recording element from the montage on the affected(ipsilateral/right) side, as well as 2) the matched derived syntheticbipolar channels from the unaffected (contralateral/left) side, thusmaintaining symmetry of analysis and data display between the twohemispheres.

FIG. 15 provides a basic overview of signal processing and displayassociated with the system. Raw electrical signals are transmittedthrough a connection cable (1500) to an interface element (1510) whichcontains signal amplifiers, basic filters and analog-to-digitalprocessing functions. The digitized signal is then transmitted to theprocessor element (1520) which performs an initial function to organizeand interpret signal data through specific montages predetermined forparticular array configurations as identified by the clinician user foran individual patient (1530). Data channels thus identified arecontinuously interrogated by a signal analysis function (1540) whichutilizes a range of quality control measures to identify “good” and“bad” (if any) recording elements. In cases where no bad recordingelements are identified, the processor provides the “true” data forreview and quantitative analysis (1550) with display of “true”referential EEG signals and “true” synthetic bipolar channels derivedfrom the input channels (1560). In cases where the quality controlelement (1540) identifies a “bad” contact (1560), associated referentialEEG signals and the associated synthetic channels are modified by theprocessor to exclude data derived from the “bad” contact along with thematched channels on the contralateral array (1570) to provide “modified”referential EEG data and “modified” synthetic bipolar channels (1580).Data from either the “true” analysis or the “modified” analysis are thusavailable for subsequent valid symmetry analysis between the twohemispheres (1590).

DETAILED DESCRIPTION OF THE INVENTION

The following definitions are provided for specific terms which are usedin the following written description.

Definitions

As used in the specification and claims, the singular form “a”, “an” and“the” include plural references unless the context clearly dictatesotherwise.

The present invention can “comprise” (open ended) or “consistessentially of” the components of the present invention. As used herein,“comprising” means the elements recited, or their equivalent instructure or function, plus any other element or elements which are notrecited. The terms “having” and “including” are also to be construed asopen ended unless the context suggests otherwise.

The term “about” or “approximately” means within an acceptable range forthe particular value as determined by one of ordinary skill in the art,which will depend in part on how the value is measured or determined,e.g., the limitations of the measurement system. For example, “about”can mean a range of up to 20%, preferably up to 10%, more preferably upto 5%, and more preferably still up to 1% of a given value.Alternatively, particularly with respect to biological systems orprocesses, the term can mean within an order of magnitude, preferablywithin 5 fold, and more preferably within 2 fold, of a value. Unlessotherwise stated, the term “about” means within an acceptable errorrange for the particular value, such as ± 1-20%, preferably ± 1-10% andmore preferably ±1-5%. In even further embodiments, “about” should beunderstood to mean+/-5%.

Where a range of values is provided, it is understood that eachintervening value, between the upper and lower limit of that range andany other stated or intervening value in that stated range isencompassed within the invention. The upper and lower limits of thesesmaller ranges may independently be included in the smaller ranges, andare also encompassed within the invention, subject to any specificallyexcluded limit in the stated range. Where the stated range includes oneor both of the limits, ranges excluding either both of those includedlimits are also included in the invention.

All ranges recited herein include the endpoints, including those thatrecite a range “between” two values. Terms such as “about,” “generally,”“substantially,” “approximately” and the like are to be construed asmodifying a term or value such that it is not an absolute, but does notread on the prior art. Such terms will be defined by the circumstancesand the terms that they modify as those terms are understood by one ofskill in the art. This includes, at very least, the degree of expectedexperimental error, technique error and instrument error for a giventechnique used to measure a value.

Where used herein, the term “and/or” when used in a list of two or moreitems means that any one of the listed characteristics can be present,or any combination of two or more of the listed characteristics can bepresent. For example, if a composition is described as containingcharacteristics A, B, and/or C, the composition can contain A featurealone; B alone; C alone; A and B in combination; A and C in combination;B and C in combination; or A, B, and C in combination.

As used herein, the term “determining” encompasses a wide variety ofactions. For example, “determining” may include calculating, computing,processing, deriving, investigating, looking up (e.g. looking up in atable, a database or another data structure), ascertaining and the like.Also, “determining” may include receiving (e.g. receiving information),accessing (e.g. accessing data in a memory) and the like. Also,“determining” may include resolving, selecting, choosing, establishingand the like.

As used herein, “implantable subgaleal electrode array”, “implantableelectrode array”, and “implantable array” are used interchangeably. Theimplantable electrode array is designed to pass through the skin and beimplanted into the subgaleal space. The implantable electrode arraycomprises one or more recording element(s), a reference element, and aground element. These elements may be constructed of metal, plastic, orother compounds.

As used herein, a “reference element” refers to a contact (preferablyalso made of metal) designed to act as a common member of variableelectrode pairs as a control allowing for the comparison of subgalealbrain activity detected by one or more recording elements on theimplantable array. For example, the reference sensor can allow forcomparison of subgaleal brain activity detected by multiple recordingelements.

As used herein, a “ground element” refers a recording element whichserves to provide information about globally recorded electrical signalsthat derive from non-physiological sources (such as local electricalequipment) and therefore allow for common-mode rejection of suchnon-physiological signals.

As used herein, a “recording element” is a contact which is capable ofdetecting subgaleal brain electrical activity. Preferably, the recordingelement is metallic.

As used herein, the “subgaleal space” refers to the anatomic compartmentof the scalp which lies below the epidermis and galea aponeurosis (thefascial layer of the scalp) and the periosteum and bone of the skull.The subgaleal space is a naturally occurring, avascular region that canbe easily accessed and traversed using specialized tools without risk ofsignificant injury, bleeding, risk of intracranial infection, or othermajor medical complication.

As used herein, the “support structure” refers to a structure (a)capable of housing the reference, the ground and the recording elements;(b) capable of transmitting the electrical signal generated by the brainto the associated processor; and (c) capable being inserted through theskin and maintained in the subgaleal space. The support structure may bedesigned for passage through a separate piece of equipment that istunneled through the subgaleal space, or the support structure itselfmay contain the necessary elements to allow for independent passage.

As used herein “circumferential arrangement” is defined as fullywrapping around the support structure so that geographically specificelectrical signals (for example those originating only on one side ofthe array) can be recorded no matter the rotational position of thearray in relation to the electrical signal. This therefore allows forpandirectional recordings with optimal tissue contact and/or eliminatesneed for a specific orientation of the device within the subgalealspace.

As used herein “directional tunneling” refers to passage of an arrayfrom a specific entry point in an anatomically relevant manner to allowrecording of brain signals of interest. For example, an array that isdirectionally tunneled from the back of the head to the front of thehead (i.e. the parasagittal plane) will allow for recording of thefrontal and parietal lobes, while an array that is directionallytunneled from the medial aspect of the head to the lateral aspect of thehead (i.e. the coronal plane) will allow of recording from a single lobe(e.g. frontal lobe, parietal lobe) in isolation depending on theanterior/posterior position of the trajectory.

As used herein, the “array exit point” refers to the point on the scalpwhere an electrode array leaves the subgaleal space, traverses theoverlying tissues and exits the scalp to the outside environment.

As used herein, “contralateral arrays” refer to arrays that areimplanted on the opposite side of the head from the array of interest(which by convention is termed the ipsilateral array).

As used herein, a “sheath” refers to a hollow structure of a diameterdesigned to accommodate an electrode array that allows for passage ofthe array through the subgaleal space in a manner that is minimallytraumatic to the surrounding tissues and the array itself. The sheathmay be made out of a flexible plastic (e.g. silastic or polyurethane),metal or another material and may either be disposable or re-usable. Thesheath may be cylindrical to allow for atraumatic passage through thetissues of the scalp but may adopt other conformations to accommodatealternate array designs.

As used herein, a “needle” refers to a piece of hardware with a sharpaspect designed to penetrate the scalp in minimally traumatic fashion.The tip may be tapered to a point to minimize the “cutting” orlaceration of the scalp and minimize the resulting size of an entry orexit point from the scalp. The needle may be cylindrical to minimizeinjury to the tissues of the scalp but may also adopt other specificconfirmations related to the design of a particular array or associatedsheath. The diameter may range from as small as 0.5 mm, 0.6 mm, 0.7 mm,0.8 mm, 0.9 mm, or 1.0 millimeter to up to 1 cm, 2 cm, or 3 centimeters.The needle may be metal or plastic in origin and has materialcharacteristics that are stiff enough to allow for directional tunnelingbut may be flexible enough so that shaping of the needle prior to orduring insertion allows for optimal passage with the natural curvatureof an individual skull. The needle may include modifications that assistwith passage through the tissue of the scalp, for example a removableattachment that can augment a clinician’s ability to “push” or “pull”the needle through the tissue of the scalp.

As used herein, an “insertion guide” refers to a structure capable ofidentifying the anatomically appropriate area for electrode entry. Forexample, an array that is intended to be inserted in the parasagittalplane overlying the watershed zone between the major vascularterritories of the frontal and parietal lobes would be best placed in aline that is externally continuous with the pupil or lateral canthus ofthe eye. The insertion guide in this case would allow the user toidentify the proposed linear position of entry and exit points alongthis line on the scalp. In addition, the insertion guide may providereference points to the clinician regarding the optimal insertion andelectrode points for an array based on the natural points of curvatureof the human skull, notably at the mid-parietal and mid-frontal regions.

As used herein, a “retention means”, “retention device” or “retentionelement” refers to a structure that either permanently or temporarilyaffixed to the implantable electrode array, that can be secured to theskin or otherwise positioned to prevent the array from being dislodgedor pulled through at the exit site from the skin. With some embodimentsof the invention, the retention means may be easily removed tofacilitate bedside removal of the array. Such retention means can bepositioned either at the skin entry site or exit site (or both) andensures appropriate placement and positioning of the implantable device.Examples of such retention means, include but are not limited to 1)plastic “stoppers” that attach to the end of an array that may cover anentry site, attach to the skin and firmly secure the array from furtherforward movement, or 2) plastic discs that may be placed over the arraythat limit array movement by friction and can be secured to the scalp toprevent backwards movement of the array into the subgaleal space. Inaddition, the retention means can serve to cover the insertion and exitpoints and provide for greater sterility of the array within thesubcutaneous tissues. The retention means may either be permanentlyaffixed to the array (e.g. physically part of the support structure) orseparately applied to the array during or after an insertion procedure.The retention means may also be integrated with the interface and/orprocessor, such that the interface and/or the processor are included aspart of the retention means.

As used herein, an “exit guide” refers to a structure that serves to“catch” the needle and/or sheath to optimize exit of the array from thepreferred exit point from the subgaleal space to the externalenvironment. The exit guide can allow the clinician to target a specificexit point on the scalp and provide a physical means by which the needleand/or sheath are physically targeted to the intended exit point. Thiscan be accomplished through a combination of pressure from the exitguide on the scalp surrounding the proposed exit point with a centralarea in the exit guide which encompasses the proposed exit point wherethere is no pressure on the underlying scalp. The exit guide may becircular in shape with a central hollow region through which passage ofthe needle, sheath and/or array occurs. The exit guide may becircumferentially tapered towards the central hollow region to assist inneedle passage through the skin.

As used herein, a “montage” refers to a specific manner in whichrecorded electrical signals are displayed. A montage may bepredetermined by the processor or may be user-defined. The montage canbe altered to include recordings from particular electrode pairs ofinterest and may display electrical signals as initially recorded(“referential channels”) or signals that are generated through secondarymathematic combinations of referential recordings (“syntheticchannels”). In this manner, a “recording montage” or a “referentialmontage” refers to signals derived in primary fashion based on thespecific relative locations of the recording elements to the referenceelectrode and the relative position of an individual recording elementalong an array, while a “bipolar montage” is a display utilizingmathematical comparisons of referential recordings from separaterecording elements of interest along one or more arrays.

As used herein, a “processor” is capable of modifying, analyzing,correlating, storing and displaying recorded subgaleal brain electricalactivity. The processor may comprise hardware and/or software elements.

As used herein, “subgaleal brain activity” is defined as the electricalsignals generated by the brain that are recorded from within thesubgaleal compartment of the brain. As described herein, “subgalealbrain activity” or “subgaleal brain electrical activity” can be measuredby a variety of different parameters capable of detecting and/ormeasuring electrical activity, including, but not limited to: (a)average voltage level; (b) root mean square (rms) voltage level and/or apeak voltage level; (c) derivatives involving fast Fourier transform(FFT) of recorded brain activity, possibly including spectrogram,spectral edge, peak values, phase spectrogram, power, or power ratio;also including variations of calculated power such as average powerlevel, rms power level and/or a peak power level; (d) measures derivedfrom spectral analysis such as power spectrum analysis; bispectrumanalysis; density; coherence; signal correlation and convolution; (e)measures derived from signal modeling such as linear predictive modelingor autogressive modeling; (f) integrated amplitude; (g) peak envelope oramplitude peak envelope; (h) periodic evolution; (i) suppression ratio;(j) coherence of calculated values such as spectrogram, spectral edge,peak values, phase spectrogram, power, and/or power ratio; (k) wavelettransform of recorded electrical signals, including spectrogram,spectral edge, peak values, phase spectrogram, power, or power ratio ofmeasured brain activity; (I) wavelet atoms; (m) bispectrum,autocorrelation, cross bispectrum or cross correlation analysis; or (n)waveform phase reversal, or other alteration of waveform characteristicsrelated to dipole, resulting in variable positive or negative valuesbetween recording elements and reference sensors at specific moments intime. In preferred embodiments, the subgaleal brain activity is measuredby categorical measurements, such as, for example, from volts (V), hertz(Hz), and/or or derivatives and/or ratios thereof.

As used herein, the system can provide information regarding subgalealbrain activity in a “continuous” and/or in a “real-time” fashion,allowing for optimized detection of brain activity.

As used herein, the implantable subgaleal array is designed fortemporary (i.e., minutes to hours), acute (i.e., hours to days), orsemi-chronic (i.e., days to weeks) implantation in a patient.

As used herein the recording element may be positioned “in proximitywith” other elements on the implantable array. “In proximity with” isdefined as “at, within or associated with” the specified element.

It will be further understood that when an element is referred to asbeing “on”, “attached”, “connected” or “coupled” to another element, itcan be directly on or above, or connected or coupled to, the otherelement or intervening elements can be present. In contrast, when anelement is referred to as being “directly on”, “directly attached”,“directly connected” or “directly coupled” to another element, there areno intervening elements present. Other words used to describe therelationship between elements should be interpreted in a like fashion(e.g., “between” versus “directly between,” “adjacent” versus “directlyadjacent,” etc.).

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper” and the like may be used to describe an element and/or feature’srelationship to another element(s) and/or feature(s) as, for example,illustrated in the figures. It will be understood that the spatiallyrelative terms are intended to encompass different orientations of thesystem in use and/or operation in addition to the orientation depictedin the figures. For example, if the system in a figure is turned over,elements described as “below” and/or “beneath” other elements orfeatures would then be oriented “above” the other elements or features.The system can be otherwise oriented (e.g., rotated 90 degrees or atother orientations) and the spatially relative descriptors used hereininterpreted accordingly.

Implantable Subgaleal Electrode Array

We have developed systems and methods by which an implantable subgalealelectrode array can be inserted at the bedside into the subgaleal spaceof a patient by clinical personnel to provide continuous high-fidelityEEG recording. Examples have been provided in the Figures as describedabove.

In further examples (not shown), the reference element and/or the groundelement may be in the form of a wire extending longitudinally along thearray.

The array, such as array (250) shown in FIG. 2 , is specificallyconfigured and positioned to gather hemispheric EEG data, a capabilitythat is of relevance for patients with brain injury. An associatedexternal processor element, such as the processor element (1520) shownin FIG. 15 , can be configured to record aspects of the array, includingpreassignment of the ground and reference electrodes. Suchconfigurations can minimize the need for technical expertise ininitiating and maintaining the recording derived from the array and, insome circumstances, can limit the number of wires that are associatedwith the patient. In preferred embodiments, the system automaticallymonitors the fidelity of signal from individual recording elements toensure that the recorded electrical activity is valid. In cases wherebilateral arrays are deployed the system will “balance” the recordingmontage should there be specific non-functional recording elements onone side or the other that may influence evaluation of EEG symmetrybetween the two cerebral hemispheres.

The approach of placing the array in the subgaleal space takes advantageof specific characteristics of this anatomic location for temporarytargeting of devices in the clinical setting by personnel with nospecialized surgical training or prior experience with electrodeimplantation. There are no major blood vessels or other sensitivetissues in this region that could be injured and result in clinicalcomplication. In preferred embodiments, the method requires no incisionas the array can be implanted into the subgaleal space using a needleand therefore, limits the risk of infection associated with deviceplacement. In this embodiment, as the insertion technique requires onlya needle for placing the arrays there is no need for a patient to betaken to the operating room for device insertion, allowing the procedureto be performed at the bedside in the intensive care unit, in theemergency room, in an ambulance en route the hospital, or in a patient’shome etc. In other preferred embodiments, the use of the needle alongwith an associated sheath to pass the electrode through the skinminimizes trauma to the traversed tissues and minimizes the chance ofsubgaleal “pocket” formation as may occur with the use of a largertrocar (thereby leading to potential poor contact of the electrode arraywith the surrounding tissues).

Other benefits of the use of the implantable subgaleal electrode arrayas described herein include a low risk of developing systemic infectionshould there be a local infection with an implanted array, as there isno involvement of a major fluid compartment (such as the cerebrospinalfluid) or intravascular space. In cases where a local infection issuspected, the method of insertion and stabilization allows for easybedside removal the devices without the need for a formal surgicalprocedure. The presence of the underlying skull prevents any possibilityof brain injury during insertion. The natural plane of separationbetween the galea and the underlying skull makes passage of a devicevery easy in this plane, therefore requiring no specialized anatomicknowledge or surgical training.

Moreover, insertion of the implantable electrode array into thesubgaleal space takes advantage of conserved similarities in humancranial and brain anatomy, notably the position of the largest lobes ofthe brain (frontal and parietal), the specifics of cranial proportionsand commonalities of the major regions of blood supply. Positioning theimplantable array as described herein provides coverage over the lateralbulk of the frontal and parietal lobes which is typically the“watershed” zone between major blood vessels supplying the majority ofthe brain (anterior cerebral artery and middle cerebral artery). This isthe region that is at greatest metabolic risk in cases of decreasedblood flow due to inherent limitations of flow and is therefore ofgreatest interest for EEG monitoring.

Means for Implantation and Maintenance of the Implantable Arrays

As described herein, implantable electrode arrays are designed forinsertion at the bedside by clinical personnel without specializedsurgical expertise. Moreover, in preferred embodiments, the describedarrays are designed for temporary use (e.g., for example minutes toweeks), can be easily removed at the bedside (for example in cases wheresubgaleal EEG is recording is no longer clinical indicated), and can beinserted using only local anesthetic with minimal risk to the patient,as placement is outside the skull, no major anatomic structures are atthreat, and the array is not placed within access to the blood stream orother fluid compartments with physiological extension to the body orbrain.

In preferred embodiments, the implantable array is designed to be passedin a linear parasagittal plane in an anterior-posterior orientation inthe ipsilateral pupillary line to allow for anatomically relevanthemispheric monitoring. In such cases the “insertion” guide would assistthe clinician in identifying the appropriate entry and exit points forthe array prior to passage of the array through the subgaleal space andoptimize subsequent electrode positioning in the parasagittal line ofinterest. In some cases the insertion guide could be an L-shaped toolwith a 90-degree elbow designed to be physically placed on the skull inline with the pupillary line, which will allow the clinician to 1)confirm the planned trajectory of the implanted array, 2) mark the entrypoint at the parietal or frontal curvature of the skull (which would beidentified on the scalp as the point representing the 45 degree anglefrom the elbow of the insertion guide), and 3) mark the proposed exitpoint at the frontal aspect of the scalp which would allow for theentirety of the length of the implanted array to reside within thesubgaleal space (based on the known length of the array itself). Anexample of such a tool in the form of a needle insertion guide (750),are shown FIGS. 7A and 7B.

In other preferred embodiments, the system includes additional hardwareused to streamline and simplify insertion technique. For example, thesystem could comprise a needle to pass the implantable array into thesubgaleal space such as the needles 300, 320 and 330 shown in FIGS. 3A,3B and 3C. In such embodiments, the needle could have a tapered tip tominimize injury to skin and subcutaneous tissues. The needle could alsohave a curve at the end to facilitate passage into and out of thesubgaleal space, and there may be a hollow sheath attached to the needlethrough which the array is passed to be deployed in the subgaleal space.In some embodiments, the needle may be inserted at one point and exit ata second point or it may be hollow and only enter for deposition of thearray within the subgaleal space. Additionally, the array may includetemporary plastic “stoppers” to be placed at entry and/or exit points tosecure the implantable array to the skin. Such stoppers may also includethe interface and/or the processor. In some embodiments, the needle mayhave a removable cross-piece that assists with push and pull aspects ofthe insertion procedure.

In some cases, such as where a shorter array is of potential use, it maybe deployed using a hollow needle where there is a single point ofinsertion without a secondary exit through the skin; in this case theneedle would be passed into the subgaleal space and the implantableelectrode array is inserted through the needle, with the needlesubsequently withdrawn over the electrode array and a stopper thenapplied to secure the electrode in place.

Other preferred embodiments include an “exit guide” that assists theclinician with localizing and optimizing passage of the needle, sheathand/or array from the desired exit point through the scalp. An exampleof such an exit guide 600 is provided in FIG. 6A.

Associated Hardware

In preferred embodiments, external hardware to which a single lead fromeach implantable electrode array can be connected toamplify/digitize/filter recorded EEG signals

As described herein, the connected processor is capable of recording,analyzing, and displaying raw EEG signals from arrays

In preferred embodiments, the processor includes predetermined“templates” that the user can select depending on the specific nature ofthe arrays implanted in a particular patient (unilateral, bilateral,etc) and are critical for identifying the appropriate reference, groundand recording elements. For example, in cases where bilateral subgalealarrays are deployed and appropriate template is selected by the user,the ground element may be identified by the processor as the most distalcontact from the array exit point on one array while the reference isthe most distal contact on the other array. In another representativeexample where a unilateral subgaleal array may be deployed, the templatemay identify the ground element as the most distal contact from thearray exit point and the reference element as the most proximal contactfrom the array exit point. In other embodiments, templates may beavailable that are specific for arrays encompassing different numbers ofrecording elements with divergent spacing between recording elements.The existence of these templates thus allows the user to avoid the needto input specifics of the ground element, reference element, orrecording elements on a patient-by-patient or array-to-array basis. Morespecifically, this allows the user to have no specialized knowledge ortechnical skill with the art of EEG to provide durable and effectivefunctional EEG recording from subgaleal arrays.

In further preferred embodiments, the processor includes a real-timeanalytical function which interrogates qualities of electrical signalsfrom individual recording elements on the array to confirm the veracityof recording, and if poor signals are recorded (i.e. extremely lowamplitude indicating lack of contact with tissue or an incorrectlyconnected array, or extremely high amplitude indicating electricalartifact generated by non-physiological sources) the processoridentifies that contact as a “bad channel.” The user can thus be warnedto pursue simple interventions to ensure that an array of interest isappropriately connected. In other cases, the processor wouldautomatically switch use of recording elements to those providingelectrophysiologically appropriate signals. Through this continuousmonitoring and potential switching activity the processor thereby 1)providing an immediate and automated method to confirm high-fidelityreference and ground channels which are essential for effective EEGrecording; 2) allows the user to have no specialized knowledge orexperience with the technical aspects of EEG recording; and 3)automatically maintains maximum fidelity of EEG recording throughout arecording period without need to replace or monitor the fidelity of thereference or ground lead or specific recording elements along an array.

In some cases the processor may display and store EEG data in a bipolarreferential montage, whereby adjacent contacts are mathematicallycompared to provide bipolar referencing for analysis. In some casesbipolar referential comparisons may use a “skip one,” “skip two” or“skip more” approach to provide greater geographic coverage of theunderlying brain. Such bipolar comparisons are generated throughmathematical combination of the referential recordings from specificrecording elements (i.e. the common reference recordings) to derive asynthetic electrical signal that is representative of the difference inelectrical activity in the geographic region of the brain subtended bythe two recording elements included in the bipolar comparison.

In additional embodiments, the processor will include analyticalfunctions that perform automated quantitative analysis on recorded EEGsignals; such analysis may include derivatives involving fast Fouriertransform (FFT) of recorded brain activity, possibly includingspectrogram, spectral edge, peak values, phase spectrogram, power, orpower ratio; also including variations of calculated power such asaverage power level, rms power level and/or a peak power level; measuresderived from spectral analysis such as power spectrum analysis;bispectrum analysis; density; coherence; signal correlation andconvolution; measures derived from signal modeling such as linearpredictive modeling or autogressive modeling; integrated amplitude; peakenvelope or amplitude peak envelope; periodic evolution; suppressionratio; coherence and phase delays; wave let transform of recordedelectrical signals, including spectrogram, spectral edge, peak values,phase spectrogram, power, or power ratio of measured brain activity;wavelet atoms; bispectrum, autocorrelation, cross bispectrum or crosscorrelation analysis; data derived from a neural network, a recursiveneural network or deep learning techniques; or identification of aregion of an array detecting local minimum or maximum of parametersderived from any of the above

In cases of bilateral monitoring, the processor will also include a“balancing” function that includes and displays equivalent channels fromeach array in order to provide symmetrical data for each hemisphere ofthe brain. Maintaining symmetry of data acquisition and display can becritical when a clinician desires to compare aggregate electricalactivity on the two sides of the brain in order to identify possibleasymmetry of electrical activity. For example, in cases where injury orneurophysiological aberration may affect one side of the brain(“unilateral abnormality”), there may be diminished or otherwise alteredbrain electrical activity in the affected hemisphere in comparison tothe contralateral (“unaffected”) hemisphere. In contrast, in cases whereboth hemispheres are affected in equivalent fashion by injury orphysiological aberration (“bilateral abnormality”) it would be expectedthat signals from both hemispheres would be symmetrically decreased.However, such analysis requires that the nature of source data isequivalent between the two hemispheres (e.g. is data recorded from thesame anatomic locations and electrographic “fields”); any asymmetry ofelectrode location or distance can lead to spurious comparisons. Incases where a particular recording element on one array may be excludedby the processor, the “balancing” function of the processor wouldsimilarly exclude data from the matched recording element on thecontralateral array to ensure symmetry of data input for subsequentanalysis.

The invention is not limited to the embodiment herein before describedwhich may be varied in construction and detail without departing fromthe spirit of the invention. The entire teachings of any patents, patentapplications or other publications referred to herein are incorporatedby reference herein as if fully set forth herein.

1-14. (canceled)
 15. A system for detecting and/or transmittingsubgaleal electrical signals, comprising: at least one subgalealelectrode array including: a flexible support structure having a shapeimplantable into and configured to conform to a shape of a subgalealspace of a patient; and a plurality of electrodes distributed along alength of the flexible support structure, each of the plurality ofelectrodes arranged circumferentially about the flexible supportstructure, and the plurality of electrodes configured to one or more ofdetect or transmit a subgaleal electrical signal; and an interfaceconfigured to electrically connect the plurality of electrodes to anexternal processor.
 16. The system of claim 15, further comprising: aneedle including a tip that is tapered and that is straight or angled,the needle operable to insert the at least one subgaleal electrode arrayinto the subgaleal space without an incision.
 17. The system of claim16, wherein the needle further includes a curved portion extending fromthe straight or angled tip.
 18. The system of claim 16, wherein: theneedle is formed from a material having sufficient stiffness to enabledirectional tunneling of the needle within the subgaleal space; and thematerial further has a sufficient flexibility to enable shaping of theneedle one or more of prior to or during insertion of the needle intothe subgaleal space.
 19. The system of claim 16, wherein the needle isintegral with the at least one subgaleal electrode array.
 20. The systemof claim 16, further comprising: a sheath having: a hollow structureconfigured to enable passage of the at least one subgaleal electrodearray therethrough; and at least one hole from an exterior of the sheathinto the hollow structure, the at least one hole configured to enabledeployment of the at least one subgaleal electrode array out from thehollow structure and into the subgaleal space.
 21. The system of claim20, wherein the needle is integral with the sheath.
 22. The system ofclaim 15, further comprising: at least one stopper that is configured toattach to an end of the at least one subgaleal electrode array and tothe patient at an entry or exit site of the end so as to inhibitmovement of the at least one subgaleal electrode array.
 23. The systemof claim 22, wherein the at least one stopper, in a state of attachmentto the end of the at least one subgaleal electrode array and to thepatient, is configured to cover the entry or exit site and maintain asterility of the insertion of the at least one subgaleal electrodearray.
 24. The system of claim 22, wherein the at least one stopper isintegral with the interface.
 25. The system of claim 15, furthercomprising: the external processor, wherein the external processor isconfigured to perform operations, including: monitoring the plurality ofelectrodes of the at least one electrode array for an indication that anelectrode of the plurality of electrodes is providing undesirable signalquality; and responsive to the monitoring, excluding a recording channelof the at least one electrode array providing the undesirable signalquality.
 26. The system of claim 25, wherein the external processor isintegral with the at least one stopper.
 27. The system of claim 25,wherein the external processor is integral with the interface.
 28. Asystem for detecting and/or transmitting subgaleal electrical signals,comprising: at least one subgaleal electrode array including: a flexiblesupport structure having a shape implantable into and configured toconform to a shape of a subgaleal space of a patient; and a plurality ofelectrodes distributed along a length of the flexible support structure,each of the plurality of electrodes arranged circumferentially about theflexible support structure, and the plurality of electrodes configuredto one or more of detect or transmit a subgaleal electrical signal; aninterface configured to electrically connect the plurality of electrodesto an external processor; a needle including a tip that is tapered andthat is straight or angled, the needle operable to insert the at leastone electrode array into the subgaleal space without an incision; and atleast one stopper that is configured to attach to an end of the at leastone electrode array and to the patient at an entry or exit site of theend so as to inhibit movement of the at least one electrode array. 29.The system of claim 28, further comprising: a passage assistantattachment configured to one or more of push or pull the needle throughthe subgaleal space.
 30. The system of claim 28, further comprising: aninsertion guide usable to identify an anatomically appropriate area forinsertion of the at least one subgaleal electrode array.
 31. The systemof claim 28, wherein the at least one stopper includes a first retentionelement configured to be located at a skin entry site.
 32. The system ofclaim 31, wherein the at least one stopper further includes a secondretention element configured to be located at a skin exit site.
 33. Thesystem of claim 28, further comprising: an exit guide configured tofacilitate passage of the needle through a skin layer at an-exit point.34. A system for detecting and/or transmitting subgaleal electricalsignals, comprising: at least one subgaleal electrode array including: aflexible support structure having a shape implantable into andconfigured to conform to a shape of a subgaleal space of a patient; anda plurality of electrodes distributed along a length of the flexiblesupport structure, each of the plurality of electrodes arrangedcircumferentially about the flexible support structure, and theplurality of electrodes configured to one or more of detect or transmita subgaleal electrical signal wherein: the plurality of electrodesincludes at least one reference electrode, at least one groundelectrode, and one or more recording electrodes; an interface; a firstportion of the flexible support structure includes the one or morerecording electrodes, and a second portion of the flexible supportstructure includes the reference electrode and the ground electrode,with no recording electrodes between the second portion and a first endof the at least one electrode array; and an interface; and an externalprocessor electrically connected to the interface, wherein the externalprocessor is configured to perform operations, including: monitoring theplurality of electrodes of the at least one electrode array for anindication that an electrode of the plurality of electrodes is providingundesirable signal quality; and responsive to the monitoring, excludinga recording channel of the at least one electrode array providing theundesirable signal quality.